This paper addresses the general issue of software tool support for designers, helping them to structure, to communicate and to document activities of generation, evaluation and decision. Here the focus is on detailed consideration of desired and undesired behavioural relationships among elements of complex design artefacts and with end users. This is an area that has recently been under discussion by proponents and critics of Affordance Based Design methods. Our solution approach is to extend an existing graph based software tool for design rationale capture that has been in widespread use in an international aerospace company for several years. We are integrating its Issue Based Information System (IBIS) based design argumentation with hierarchical Functional Analysis Diagrams (FAD), a form of Concept Map. The resulting software is being tested by practical application on pilot projects in the company, and initial experiences have been very favourable. The new graph element types, bidirectional relationship types between graphs, and supporting navigational facilities are described. Their use is illustrated by example of an integrated hierarchical FAD and assembly geometry model of a gas turbine engine.

DRed is a graphical software tool for design rationale capture that, despite essentially still being a research prototype, has proved robust and useful enough gradually to achieve widespread use in an international aerospace company. The main areas of application up until now have been: (1) in the early stages of design; (2) in the root cause analysis and design of solutions to problems occurring while a product is in service. In order to lay out and navigate freely large interlinked rationales across multiple charts, DRed uses a simple bidirectional hyperlinking approach known as tunnel linking. In this paper we suggest that if it could be made easy for users to create bidirectional hyperlinks between DRed elements and selected locations in a range of external document types, then this might support the capture not just of the rationale, but of a unified, easily navigable information space covering the specification, rationale, calculations, design tasks and the emerging product definition. The objective of this research was to devise a practical way of implementing such a facility, then to explore how integrated design information spaces captured in this way might be structured, and to assess the feasibility of their capture as the design proceeds. To be successful, this will require extending the routine use of DRed from the conceptual into the embodiment design phase. Thus the case study in this paper focuses on the embodiment design of a simple mechanical transmission.